Our findings confirm that subjects with active myofascial trigger points (MTrPs) have a significantly different biochemical profile (i.e., elevated levels of pro-inflammatory mediators, neuropeptides, cytokines, and catecholamines) within the local milieu of the MTrP compared to those without MTrPs or those with a latent (non-symptomatic) MTrP. These classes of substances are known to be associated with chronic pain states. Furthermore, we found significant differences in analyte levels at needle insertion between the trapezius and unaffected gastrocnemius in the Active group, suggesting that the vicinity of the active MTrP exhibits a unique biochemical milieu of substances associated with pain and inflammation. Additionally, gastrocnemius analyte levels were higher in the Active group than either the Latent or Normal groups. This further suggests that analyte abnormalities may not be limited to local areas of active MTrPs in the upper trapezius but may also be present at sites remote from the active MTrP. The MTrP is a palpable, discreet, localized tender spot in a taut band of skeletal muscle. In spite of the high prevalence, there are currently no imaging criteria for the diagnosis of MTrPs or for assessing clinical outcome of treatments. Accordingly, the diagnosis of myofascial pain is based exclusively on history and physical examination. Our preliminary findings using diagnostic ultrasound imaging and vibration sonoelastography suggest that MTrPs can be differentiated from surrounding muscle based on differences in echogenicity measures of tissue stiffness and local muscle blood flow properties. It is unclear how the symptoms and physical findings of MTrPs and uninvolved muscle behave over time; they could improve, worsen or remain stable. It is suspected that the symptoms and physical findings of MTrPs will change over time, and we intend to correlate any clinical changes with local biochemical analyte levels, viscoelastic properties of the MTrP and unaffected tissue and local muscle blood flow properties.